Excavation installation

ABSTRACT

The invention relates to an excavation installation, comprising excavation means ( 1,2 ) in which more than one excavation means ( 1,2 ) is positioned offset next to another in a row ( 34,35 ) of excavation means ( 1,2 ). In use the excavation installation may excavate a horizontal bottom of water ( 102 ) in a direction that is perpendicular to the direction of the rows ( 34,35 ) of excavation means ( 1,2 ). The excavation means ( 1,2 ) are connected to a rigid construction, in which the rigid construction ( 3 ) is positioned vertically above the excavation means ( 1,2 ). The rigid construction ( 3 ) is resiliency connected to a bridge ( 5 ) that is positioned vertically above the rigid construction ( 3 ) and connected by means of actuators ( 7 ).

The invention relates to an excavation installation comprisingexcavation means. The excavation installation is suited to excavate asubstantially horizontal sea bed or lake floor.

US2006/0032094 describes a machine for dredging having a substantiallyvertical cutting front. This machine is suited for digging a trench.

WO2014153494 describes an excavation installation for deep sea mining.The installation shows multiple rows each having two rotatable miningdrums. The installation can be lowered to the sea bed by means of acable. Although the installation may be suited for deep sea mining it isnot suited for dredging a defined part of the sea bed.

Excavation installations comprising excavation means are for exampledescribed in U.S. Pat. No. 4,084,334. This document describes a dredgerwith a cutter head for dredging the bottom of a body of water. In orderto do this, a vessel is positioned by means of anchors. A ladder isrotatably connected to the vessel, and at the end of the ladder thecutter head is positioned. This cutter head can excavate the bottomunder the ship. The problem that needs to be solved according to thispublished document is as follows. In case of swell, the vessel moves ontop of the waves. The consequence of this is that the pressure withwhich the cutter head is positioned onto the bottom fluctuates.Moreover, it is difficult to dredge the prescribed trail. The dangeralso exists that the cutter head will be damaged. This published patenttackles these drawbacks by proposing varying the length of the ladder inthe longitudinal direction. By doing this, the cutter head stays restingon the bottom in a substantially constant position while the vesselmoves up and down and/or back and forth.

WO2010/066757 describes a drag head of a trailing suction dredgerprovided with drag heads.

A problem with the prior art excavation installations is that they areless suited for dredging with a controlled vertical pressure forceworking on the excavating means. This is especially desired whendredging relative more cohesive and harder soil types. The limitingfactor of the vertical pressure is limited by the weight of theunderwater dredging unit.

The following excavation installation does not present such a drawback.

Excavation installation comprising excavation means in which more thanone excavation means is positioned next to another in a row ofexcavation means, in which multiples of such rows of excavation meansare positioned behind one another, and in which the excavation means ofa particular row are offset with regard to the excavation means of anadjacent row, such that in use the excavation installation may excavatea horizontal bottom of water in a direction that is perpendicular to thedirection of the rows of excavation means, in which the excavation meansare connected to a rigid construction positioned vertically above theexcavation means by means of a resilient connection in order to absorbthe vertical impact loads on the excavation means and to transmit theseimpacts to the rigid construction, and

in which the rigid construction is resiliently connected to a bridgethat is positioned vertically above the rigid construction, in which thebridge is connected to the rigid construction by means of linearactuators, in such a way that, during use, the linear actuators exert anadjustable and vertical pressing force onto the excavation means.

The excavation installation according to the invention enables one tocontrol and even enhance the vertical pressure of the excavation meanson the bottom of water. Furthermore, the vertical impact loads on theindividual excavation means are absorbed and transferred to the rigidconstruction. This offers the advantage that irregularities of thebottom of water can be accounted for by this construction. This meansthat the different excavation means of the excavation installation canfunction with comparable vertical pressing force, which implies thateach excavation means shall realise a comparable production. The bridgeis advantageous because it can be incorporated in a relatively fixedposition from where, in use, an adjustable and vertical pressing forcecan be exerted onto the excavation means. A further advantage is thatthe excavation installation according to the invention enables one touse multiple excavation means simultaneously, which means that a largersurface of a bottom of water can be excavated simultaneously. Duringuse, the excavation installation is moved over the bottom of water in adirection that is perpendicular to the direction of the rows ofexcavation means. By applying an offset to the excavation means in aparticular row with regard to those of the adjacently positioned row,the bottom of water can be excavated in the most efficient way possible.Parts of the bottom of water that are situated between excavation meansand that therefore cannot be excavated efficiently by the particular rowof excavation means, shall then be excavated by the excavation means ofthe adjacently positioned row.

In this description terminology shall be used such as “horizontal”,“vertical”, “longitudinal”, “above”, and “under” for describing theinvention and the preferred embodiments thereof. One thereby presupposesthe invention in its normal position under normal use, for example,during use thereof to excavate a horizontal bottom of water. By “bottomof water” one understands any surface under water that consists of asolid material. This can be a seabed or a lakebed. When using the term“longitudinal”, one refers to the direction in which the rows ofexcavation means are moved over a bottom of water. When using the term“transversal”, “transverse force”, or “transverse direction”, one refersto a direction that is perpendicular to the longitudinal direction, andthat is situated in the horizontal plane. By using the term“submersible”, one refers to the fact that a submersible constructionelement can be lowered to the bottom of water and can rise again to thewater surface.

The excavation installation can be used to excavate part of a bottom ofwater, for example in order to increase the water depth and/or toextract soil or minerals.

The number of rows of excavation means can be quite large. For example,three and preferably two rows of excavation means are positioned behindone another. The rows of excavation means are positioned behind oneanother and are positioned in a parallel way. A row of excavation meanscomprises preferably at least 2, better at least 3, and preferably atleast 4 excavation means. The maximum number of excavation means per rowwill depend on what is mechanically possible. The maximum number can forexample be 50 excavation means per row, and preferably 30 excavationmeans per row. Examples of suitable excavation means are excavationwheels, cutters, drum cutters, trailing dragheads, cutters and/orploughs.

The advantages of the invention are notably realised when the excavationmeans are rotating excavating elements, in which the excavation meanscomprise wheels that rotate around a substantially horizontal axis.Examples of such excavation means are excavation wheels and drumcutters. These rotating axes of the excavation means are positioned inthe transverse direction. More preferably, the axes of these devicesthat are positioned in one row will be positioned coaxially. It is evenmore to be preferred that such rotating excavation means are positionedpairwise in a row. The excavation means preferably comprise wheels thatrotate around a substantially horizontal axis, in which the excavationmeans are positioned pairwise in a row, and in which the rotating wheelof the first excavation means of a pair, during use, possesses arotation direction that is contrary to that of the rotating wheel of thesecond excavation means of the pair. Preferably the wheels in a rowalternate in rotation direction. The direction of the substantiallyhorizontal axis will be the direction of the row which comprises thepairs.

The rotation direction of a wheel of the excavation means in such a pairis preferably contrary to that of the other wheel of the same pair. Theexcavation means of such a pair preferably comprise a combination ofundercutting and overcutting excavation wheels. Such implementationoffers the advantage that the relatively large bending moment perexcavation wheel is compensated for at the rigid construction by theopposite moment of the other excavation wheel of the pair. Moreover, therequired force for moving a row of such excavation means over the bottomof water in the longitudinal direction is relatively small in comparisonwith a situation in which all wheels move in the same direction.

The rows of excavation means shall be part of an excavationinstallation. The excavation means are connected to a rigid constructionthat is positioned vertically above the excavation means. The rigidconstruction can be a box construction and preferably a latticeconstruction. The excavation means are connected to this rigidconstruction by means of a resilient connection, in order to absorb thevertical impact loads on the individual excavation means, and totransfer this to the rigid construction. This offers the advantage thatirregularities of the bottom of water can be accounted for by thisconstruction. This means that the different excavation means of theexcavation installation can function with comparable vertical pressingforce, which implies that each excavation means shall realise acomparable production. The excavation means themselves can also comprisemeans that transfer the local irregularities of the bottom of water toindividual excavation means. This excavation means can then,independently of the other excavation means, move in an upwarddirection. In this way a local irregularity can be avoided without thecomplete row of excavation means being blocked in the longitudinalmovement direction. Such a compensator for bottom irregularities canpreferably be added to each of the excavation means. Rotating excavationmeans such as excavation wheels and drum cutters are preferably equippedwith a compensator for bottom irregularities, with a spherical screenthat by means of bearings can be rotated around the rotation axis of thewheel of the excavation means, and is resiliently positioned relative tothe rigid construction, which means that, when relatively large orextreme obstacles are encountered on the bottom, the excavation meanswill be lifted up. Another possibility for avoiding large and/or extremeobstacles on the bottom of water is to connect the excavation means tothe rigid construction in such a way that it may pivot around an axis inthe transverse direction and/or around an axis in the longitudinaldirection. The pivot connections preferably comprise torsion springs tobring the excavation means back to their initial positions. If theexcavation means are positioned pairwise, as described above, it isadvantageous when the pairs of excavation means are connected pairwiseto a rigid construction that is positioned vertically above theexcavation means and is connected to the pairs of excavation means bymeans of a resilient connection in order to absorb the vertical impactloads and the continuously varying and fluctuating loads on the pairs ofexcavation means, and to transfer these to the rigid construction.

The invention also relates to an excavation installation comprising arow of rotating excavation means that are positioned pairwise in therow, and in which the excavation means of a pair, during use, rotates inan opposite direction, as can be seen from the figures and as will bedescribed hereafter more in detail. These rotating excavation meanspreferably are excavation wheels or drum cutters.

The excavation means are preferably removably connected to the rigidconstruction. This permits one to simply replace a less well-functioningexcavation means with a better functioning excavation means. It is alsopossible to for example replace the excavation wheels with drum cutters,or the drum cutters with excavation wheels. The excavation wheels or thedrum cutters can also be replaced by a trailing draghead or vice versa.

The rotating wheels of the excavation wheels and drum cutters arepreferably removably connected to the drive/drive shaft. Less wellfunctioning wheels of the excavation wheels or drum cutters can therebyeasily be replaced. The wheels can also be mutually exchanged. Becauseof this construction a relatively large space is needed on both sides ofthe wheel for the axis and drives. Underneath this space, a row ofexcavation means will excavate no or less soil. However, because a rowof excavation means is positioned behind or in front of this row with acertain offset, soil shall be excavated by this adjacently positionedrow.

Each of the excavation means can be connected to a suction tube thatdischarges the mixture of soil and water that is excavated by theexcavation means. For realizing a well balanced flow of soil/watermixture, preferably every suction tube per excavation means is connectedto the suction side of a separate pump. In case of dredging inrelatively shallow water depths the pumps are preferably fixed to therigid construction such to limit the distance between pump andexcavating means such to prevent cavitation of the pump.

At the extremities of a row or of every row preferably a freestandingexcavation means is foreseen. This excavation means can for example be awheel of drum cutters that is driven by the engine of the extremeexcavation wheel and/or drum cutter of the row. The function of thisexcavation means is to prevent the excavation installation from seizingup in the trench that is being dug by the excavation installationitself. This excavation means is preferably devoid of hoods that arepresent on the other excavation means for discharging the soil/watermixture.

In order to create a less inclined downward slope at both sides of thetrench that is being dug by the excavation installation, it is to bepreferred to also equip the excavation installation with an excavationmeans that is horizontally extendable in the direction of the row. Thisexcavation means is positioned above the row of excavation means and ispreferably part of the rigid construction. The excavation means ispreferably an excavation wheel or a drum cutter. If the rows ofexcavation means excavate the same surface of the bottom of water morethan once, the rigid construction and the excavation means will move ina downward direction. By moving the horizontal excavation means at eachdownward movement in the direction of the rigid construction a lessinclined downward slope will be created.

The aforementioned rigid construction is resiliently connected to abridge that is positioned vertically above the rigid construction. Thebridge can comprise a lattice framework. If the bridge forms part of asubmersible excavation installation it preferably consists of a boxconstruction. The box construction can for example be filled with a gasin order to be able to float or raise the excavation installation fromthe bottom of water. The bridge is preferably connected to the rigidconstruction by means of multiple linear actuators, amongst which arehydraulic cylinders, in such a way that, during use, an adjustable andvertical pressing force can be exerted onto the excavation means. Thespring constant of one or more springs by which the excavation means areresiliently connected to the rigid construction is preferably smallerthan the spring constant of one or more springs by which the rigidconstruction is connected to the bridge.

Such a bridge can be part of the floating vessel, in which the bridge isresiliently connected to the floating vessel by means of multiple linearactuators that extend in a downward direction from the floating vesseland towards the bridge. The bridge is thus substantially fixed relativeto the bottom of water and the vertical pressing force that may beexerted onto the bottom of water by the excavation means will relate tothe submersed weight of the vessel. The extremities of these actuatorsare preferably connected to the bridge and to the floating vessel bymeans of ball joints and springs. Preferably, the longitudinal directionof the row of excavation means is also the direction in which thefloating vessel moves. Preferably, the bridge is connected by means ofat least four linear actuators, the extremities of which are connectedto the floating vessel and to the bridge by means of a ball joint. Thisconnection comprises at least one spring. The connection with thefloating vessel is preferably movably connected in the transversedirection in order to compensate for the rolling movement of thefloating vessel. The connection, preferably a ball joint, is preferablymovably connected by means of a linear actuator. This actuator canmaintain the actuator that extends towards the bridge as much aspossible in a vertical position. By moving the floating vessel in adirection that is perpendicular to the rows of excavation means it ispossible to excavate a clearly defined part of the bottom of water.

In order to compensate all six kinematic motions of freedom of thefloating vessel the bridge is connected by means of at least four linearactuators, the extremities of which are respectively connected to thefloating vessel by means of three or more automatic controlled actuatorsand a ball joint and connected with the bridge by means of a ball joint.The three or more automatic controlled actuators are preferablycontrolled to keep the topside of the linear actuator, coupled with thebridge, at such a position in space that the linear actuator alwaysremains at its vertical position.

By using the aforementioned connection to the floating vessel it becomespossible to maintain the pressing force of the excavation means on thebottom of water at a reasonably constant and high level in situations inwhich the vessel moves under the influence of the swell and/or in casesof a bottom of water with irregularities. By moving back and forth thefloating vessel can excavate a bottom of water by means of theexcavation installation according to the invention. This is particularlyinteresting in cases in which the vessel cannot turn around because ofthe limited width of the fairway. Such a floating vessel, as describedabove and as can be seen in the figures, can also be implemented withjust one row of excavation means. For this reason the invention alsorelates to a floating vessel that is connected to a rigid constructionby means of linear actuators, comprising a row of 3 to 30 excavationmeans, and in which the rigid construction is positioned underneath thefloating vessel, and in which the linear actuators may be connected tothe floating vessel by means of a ball joint and spring, and to therigid construction by means of a ball joint. The rigid constructionpreferably comprises the aforementioned bridge and rigid constructionwith the row of excavation means that are connected thereto, asdescribed in this application.

Preferably the excavation means are trailing dredging heads, alsoreferred to as dragheads or trailing dragheads. For trailing dredgingheads less space will be present between the excavation means andtherefore less need for an additional row of offset excavation means inorder to effectively excavate a bottom of water.

The aforementioned linear actuators can be electromechanical actuatorsand preferably hydraulic cylinders.

The propulsion of the aforementioned vessel is realized in usingthrusters fixed to the vessel. To prevent the bridge and the herewithconnected excavation means to be dragged by the vessel thrusters,preferably additional thrusters are fixed to the rigid construction.These additional thrusters will push the excavation means forward inlongitudinal direction in addition to the drag force exercised by thevessel.

A problem that occurs when connecting the bridge to a floating vessel isthat the vertical pressing force that is being exerted onto the bottomof water by the excavation means cannot be larger than the submersedweight of the vessel. Hereafter will follow the description of anembodiment that allows a larger vertical pressing force. In thisembodiment the movable bridge can move horizontally and longitudinallyalong in the longitudinal direction positioned and parallel frameworkbeams that, in combination with two transverse beams, compose arectangular framework. By fixing such a frame to the bottom of water itbecomes possible to exert a larger vertical pressing force onto thebottom of water than that which is possible with a floating vessel.Moreover, it is possible to work in deeper waters than with anexcavation means that during the excavation is in some way connected toa floating vessel.

Such a frame comprises four corners. The term “corner” refers to anyconstruction that is suitable for being connected to the framework beamsand to the transverse beams. The construction is preferably alsosuitable for being equipped with supporting means and with anchoringmeans. The connection to the corners can for example be a boxconstruction or a lattice construction. Box constructions areinteresting because they can possibly be filled with water and gas inorder to float, submerse, or raise the framework. The corners of therectangular frame therefore preferably comprise means for anchoring theframe to the soil. These means are preferably screw anchors or suctionanchors.

The corners of the rectangular frame moreover preferably comprise asupporting means. Such supporting means are preferably one or morewheels, caterpillar tracks, or a sled. The supporting means arepreferably connected to the corners by means of linear actuators with anadjustable length. By means of these actuators the frame can be placedin the desired position relative to the bottom of water, for examplehorizontally. By using the supporting means the framework can be movedover the bottom of water while it remains in the submersed position.This is interesting in cases in which the excavation installation isdone with the excavation off the surface of the bottom of water thatlies under the installation. The excavation installation can then bemoved in a simple way to a surface of the bottom of water that stillneeds excavating. For the displacement it can be interesting that theexcavation installation also comprises one or more means for moving therectangular frame horizontally. These means can preferably be so-calledthrusters and/or the aforementioned caterpillar tracks and/or drivenwheels. If the frame is connected to a floating vessel, it isinteresting to make use of the propulsion of the floating vessel and ofthe means that are present on the frame for the displacement.

The movable bridge is preferably connected to the two transverse beamsby means of winch cables that permit a horizontal movement of themovable bridge along the two parallel framework beams. By applyingtension to the winch cables it becomes possible to move the movablebridge. Once the tension is applied, the winch cables also stabilise theform of the rectangular framework. This an advantage not only when theframework is being used during the excavation of a bottom of water, butalso during the vertical and horizontal transport of the framework.

Each of the extremities of the movable bridge preferably comprises aguiding tube. One of the two parallel framework beams pass through theopening of each of the tubes, in such a way that the movable bridge canmove in the longitudinal direction of the framework beams. The guidingtubes preferably comprise on their inner side resilient wheel setsand/or resilient rollers that, during use, can give the framework beamssix kinematic degrees of freedom relative to the guiding tube. Such animplementation is interesting for preventing the movable bridge fromseizing up during the displacement along the framework beams. Theguiding tubes can comprise at their lower parts supporting means toavoid deflection of the framework beams. Such supporting means arepreferably one or more wheels, caterpillar tracks, or sleds.

The extremities of the framework beams and the extremities of thetransverse beams are preferably resiliently and by means of a ball jointconnected to a corner on each of the four corners of the framework. Theresult of this is that the forces on the excavation means are beingtransferred not only by the resilient wheel sets in the bridge part, butalso by the springs between the framework beams and the transverse beamsand corners. If the framework is fixed to the bottom of water by meansof the aforementioned anchors a framework is created with a very stableform, maintaining the six kinematic degrees of freedom. In this anchoredposition the extreme loads on the excavation means and/or on the movablebridge can be absorbed or taken over by the framework. The optionalsupporting means are also resiliently connected to the corners to absorbimpact loads when the framework lands on the bottom of water. Thecombination of the springs and of the ball joints in the connectionswith the corners and the resilient supporting means results in aframework that is capable of following a bottom of water withirregularities, when the framework is being transported over the bottomof water. Also during the horizontal transportation of the frameworkover the bottom of water the framework maintains six kinematic degreesof freedom, which is interesting in order to absorb the forces that arethen exercised on the framework. The stable form of the framework duringthe horizontal transportation over the bottom of water is realised byprestressing the winch cables on both sides of the bridge and by theresilient guiding means that are part of the bridge part.

The above described excavation installation comprising the framework canbe connected to a floating vessel by means of linear actuatorscomprising ball joints and springs that connect the corners of theframework to the floating vessel. The excavation installation comprisingthe framework can also be used independently, for example in shallowwater. In shallow water the framework can be fixed to the bottom ofwater by means of screwing anchors, and can subsequently jack itself up.The transverse beams and the framework beams can in that situation belocated above the water surface and the rows of excavation means canexcavate the shallow bottom of water.

An excavation installation comprising the framework as described aboveis preferably submersible if the depth of water makes the use of afloating vessel less attractive and/or if a larger and/or constantpressing force on the excavation means is necessary. Therefore theframework beams, the transverse beams, the corners, and the movablebridge preferably comprise compartments that can be filled with gasand/or water in order to be able to float or submerse the excavationinstallation. During the lowering and rising of the framework, thrusterscan preferably be used to maintain the framework in the desiredorientation and to give it sufficient stability.

An excavation installation comprising the submersible framework can beused in shallow water, at normal dredging depths, and in very deepwaters. Because the framework is flexible, it can be transported veryeasily. Moreover, the excavation means can simply be replaced by anothertype of excavation means. The application of such an excavationinstallation has not yet been described and is a clear improvement overthe existing installations.

A spare excavation means can be foreseen to replace an excavation meansthat no longer functions properly. Therefore, preferably on both sidesof the rows of excavation means, one or more excavation means arepresent that can be positioned in the place of the no longer functioningexcavation means. The positioning can take place by means of cables orrails.

The energy that is needed to drive the excavation means and otherelements such as anchors, thrusters, and actuators can be electricalenergy that is transported from the mainland or from a mother vessel onthe surface of the water by means of cables. The electrical energy canalso be generated on a floating vessel by means of generators.Electricity can also be generated on the spot, under water, by using afuel cell that can for example use hydrogen or other suitable means forfuel cells. The hydrogen can be present in pressurised reservoirs. Ifsuch a pressurised reservoir has to be changed this can be simply doneby lowering a reservoir from the surface of the water to the excavationinstallation that is resting on the bottom of the water, and byreplacing the reservoirs on the spot. The energy can also be hydraulicenergy. Therefore, the excavation installation preferably comprises apressurised reservoir that can feed the necessary gas under highpressure to the systems. These reservoirs can comprise compartments withgas under pressure. By using the compartments separately, it is possibleto deliver a more constant gas pressure to the different systems. Alsothese pressurised reservoirs can be replaced by newly pressurisedreservoirs. The used reservoirs can be filled by means of compressorsthat are present at the water surface or can be transported over fromthe mainland. On the mainland the reservoirs can be filled moreefficiently with pressurised gas. The pressurised reservoirs containinggas can also be used to fill the compartments in the framework beams,the transverse beams, the corners, and the movable bridge with gas, asdescribed before. The gas is preferably air but can also be nitrogen orcarbon dioxide.

The excavation installation shall now be described in further detail,referring to the attached drawings.

FIG. 1 shows a side view of a possible embodiment of the excavationinstallation according to the invention, with two rows (34,35) ofexcavation wheels as excavation means (1, 2). The excavation wheels canoptionally comprise teeth. The excavation means (1, 2) are connected toa lattice construction (3) as the rigid construction by means of aresilient construction comprising columns (43) resiliently connected torigid lattice construction (3) by means of springs (45) as can be seenin greater detail in FIG. 5. The lattice construction (3) is positionedvertically above the excavation means (1, 2). The excavation means (1,2) are connected to a suction tube (4) that is used to discharge themixture of soil and water that is being excavated by the excavationmeans (1, 2). The lattice construction (3) is connected to a boxlikebridge (5). The boxlike bridge (5) is positioned vertically above thelattice construction (3) and connected by means of columns (6) andhydraulic cylinders (7).

The hydraulic cylinders (7) and the thereto attached columns (6) permita vertical displacement of the lattice construction (3). Therefore, thecolumns (6) are connected at the bottom side to the lattice construction(3), and the columns (6) are vertically displaceable relative to theboxlike bridge (5) by guiding them through openings (8) in the bridge(5). The hydraulic cylinders (7) are fixed to the bridge (5). The upperend of the column (6) is connected to the upper ends of the hydrauliccylinders (7) by means of a spring construction (10). The springconstruction (10) is interesting for absorbing possible impact loads onthe excavation means (1, 2). This spring construction (10) can be seenin further detail in FIG. 1a , and comprises an upper plate (11) that isconnected to the upper end of the column (6), and also comprises twosprings (12) that are connected to the upper ends of hydraulic cylinders(7). The hydraulic cylinders (7) are at their lower parts connected tothe boxlike bridge (5). By means of the hydraulic cylinders (7) the rowsof excavation means (1, 2) and the thereto connected latticeconstruction (3) can be vertically moved as can be seen in FIGS. 5a and5b . The length of the hydraulic cylinders (7) is chosen in such a waythat the desired vertical movement of the excavation means (1, 2) andthe lattice construction (3) is feasible.

The construction shown in FIG. 1 has the advantage that lateral forcesand bending moments, initiated by the forces originating from the soilon the excavation means (1, 2), are being transferred via the latticeconstruction (3) and the thereto connected vertical columns (6) to thebridge (5) that in this case has a boxlike construction. Because thebending stiffness of the columns (6) is much larger than the bendingstiffness of the hydraulic cylinder rods (7), the lateral forces andmoments shall be absorbed more or less completely by the columns (6).

FIG. 2 shows the construction of FIG. 1 in combination with asubmersible and rectangular framework (15). The framework (15) consistsof two parallel framework beams (16,17) positioned in the longitudinaldirection and two transverse beams (18, 19). The bridge (5) is movablyconnected to the framework (15) by means of a bridge part (22)comprising two guiding tubes (20, 21) as well as a partially shieldedspace (22 a) in which the excavation means (1, 2) and the latticeconstruction (3) can move vertically. The bridge part (22) is connectedto the two transverse beams (18, 19) by means of winch cables (23) thatpermit a horizontal movement of the bridge part (22) and thus of thebridge (5) along the two parallel framework beams (16, 17). Theframework beams (16, 17) pass through the guiding tubes (20, 21), as canbe seen in further detail in FIGS. 7a-c . By means of four hydrauliccylinders (5 b) the bridge (5) can be moved vertically upwards relativeto the bridge part (22). By doing this the excavation wheels can bemoved upwards, for example for carrying out maintenance work.

FIG. 2 also shows that the four corners (24-27) of the framework (15)comprise screw anchors (33 a) for anchoring the framework (15) to thebottom of the water. Each corner (24, 25, 26, 27) also comprises a sled(33) as supporting means, as well as thrusters (28) that can be used tohelp move the framework (15). The screw anchors (33 a) are driven by anengine (not represented), and are connected to the framework (15) bymeans of a column (29). The column (29) is at its upper extremityconnected to hydraulic cylinders (30) by means of a plate (31). Thecolumn (29) passes movably through an opening (32) in the corner (24).Hydraulic cylinders (30) are at their lower part connected to the corner(24).

FIG. 3 shows the excavation installation of FIG. 2, seen from the bottomupwards. The reference numbers refer to the same parts as in FIG. 2. Thetwo rows (34, 35) of excavation means (1, 2) each consist of nine drumcutters. The two rows (34, 35) are positioned adjacently. In other wordsthe rows (34, 35) are parallel and positioned next to one another. Onecan see that the nine excavation wheels of a row (34) of excavationmeans are offset relative to the nine excavation wheels of an adjacentrow (35). By doing this a continuous surface of the bottom of water willbe excavated during use when the bridge (5) is moved by means of winches(23) from a position at the transverse beam (18) in the direction of thetransverse beam (19) (or vice versa).

FIG. 4 shows the bridge (5) of FIG. 1. The reference numbers refer tothe same parts as in FIG. 1. This figure shows how the gaps between theexcavation means (1) in the row (34) are filled up with the offsetexcavation means (2) of the adjacent row (35). A continuous row of drumcutters can be seen, formed by the row (34) and by parts of the row(35). This figure also shows how the different suction tubes (36) areintegrated into the lattice construction (3) and connected to thelattice construction (3). The suction tubes (36) are resilientlyconnected to the individual excavation means (1). The suction tubes (36)converge in suction tubes (4) then in turn converge in a central suctiontube (37 a). These suction tubes (4 and/or 36) are preferably completelyor partially flexible, such that, when the rows (34, 35) of excavationmeans (1, 2) and the lattice construction (3) are hoisted up to thebridge (5) or are being lowered, the suction tubes (4) can be shortenedor extended. This can be done by the suction tubes (4 and 36) comprisingtwo telescopically sliding parts, in such a way that the suction tubesare in possession of an adjustable length . An alternative is to havethe suction tubes comprise a flexible part, for example a part with aU-form, that can absorb the vertical displacement of the suction tube.

FIG. 4 also shows a freestanding cutter wheel (34 a, 35 a) at bothextremities of the rows (34, 35), meant to avoid the excavationinstallation seizing up in its own excavated trench. Moreover, there aretwo horizontally extendable excavation means (36 a) at the top side ofthe lattice construction (3), which can be moved outwardly and inwardlyby means of hydraulic cylinders (36 b), in order to realise a planedownwardly sloping surface.

The mixture of water and solid material that is discharged via thesuction tube can be transported directly to the water surface or via atube, for example to be collected in a vessel. The mixture can also betransported to a storage tank that is positioned on the bottom of water.The thus stored mixture can then be transported from this tank orpossibly in this tank to the surface.

FIG. 5a shows how the excavation wheel (38) is resiliently connected tothe lattice construction (3) and also shows the integrated suction tube(36). FIG. 5b is a cross-section along line A-A of FIG. 5a . As eachexcavation wheel (38) is resiliently connected to the complete latticeconstruction (3) it is possible that the excavation wheels (38) can moveindependently of one another in a vertical direction relative to thelattice construction (3). FIG. 5b is a cross-section through theexcavation wheel (38) from FIG. 5a . The suction tube (36) comprises apart (37) with a smaller diameter, a part that extends right up to theexcavation wheel (38). The part (37) of the suction tube can movevertically in the opening of the suction tube (36). The part (37) of thesuction tube passes through and is connected to a boxlike construction(39). A hood (40) enhances the flow of the soil/water mixture, limitsthe pressure losses, and can be controlled and turned at the requiredangle by means of hydraulic cylinders (41) that comprise biasing springs(42). The construction is such that the hood (40) can be turned in thedirection that is opposite to the direction of movement of the row ofexcavation means. In other words, this is when the bridge arrives at oneside of the frame and subsequently returns to the opposite transversebeam. Moreover, a plunger (47) is foreseen that is used to adjust theexcavation depth of the excavation wheels (38).

On top of the boxlike construction (39) four columns (43) are foreseenper excavation wheel (38) that extend upwardly. The columns (43) passmovably through a tube like opening (44) in the lattice construction(3). Above and below the tube like opening (44) a column (43),comprising springs (45), is clamped between flanges (46). By removingthe upper flanges (46) that are positioned above the latticeconstruction (3) and that are connected to the columns (43), theexcavation wheel (38), the part (37) of the suction tube, the box likeconstruction (39), and the columns (43) can be easily dismantled, forexample to be replaced by another type of excavation means, such as thealready mentioned draghead, cutter, drum cutter, or plough.

FIG. 5c shows a cross-section of a possible drive of a rotatingexcavation wheel or drum cutter (1), in which the excavation wheel isdriven by two driving shafts (139) that are suspended on bothextremities by means of bearings (133) and are connected tosynchronously rotating engines (131), in which the engines (131) as wellas the bearings (133) are fixed to the water permeable box likeconstruction (39) by means of plate elements (130). The wheels (1) canbe replaced in a very simple way by loosening the bolts of the fixedflanged connections (136, 135). This way, the engine and/or the bearingsdo not need to be replaced. A problem with this construction is that therelatively large space remains present between the excavation wheels(1). Thanks to the configuration with the offset, as can be seen in FIG.6b , this problem is solved and the excavation means can be assembled insuch a way as to allow it to excavate a rectangular surface of thebottom of water. The part of the bottom of water that is not excavatedby row 34 shall then be excavated by row 35.

FIG. 6a shows a cluster of four excavation wheels (50), in which twoexcavation wheels (51, 52) are connected as a pair (50 a, 50 b) to awater permeable box like construction (53), whereas the two remainingexcavation wheels (54, 55) are connected as a pair to a separate waterpermeable box like construction (56) via plates (58). For wheel (55) amotor (57) is shown. The excavation wheels are in possession of ahorizontal rotating axis. The boxlike constructions (53, 56) are in turnconnected to the lattice construction (3) via a resilient connection(43) in order to absorb the impact loads and the continuously varyingand fluctuating loads on the pair of excavation means and to transmitthese impact loads to the rigid construction (3). Such a connection iscomparable to those of FIGS. 1-5. Per pair one of the excavation wheelsis overcutting, whereas the other excavation wheel is undercutting withangular velocities ω in opposite directions but preferably with the samemagnitude. With the exception of the over- and undercutting form of thecutting elements, the geometry and the positions of the cutting elementsof the excavation wheels (51, 52, 54, 55) are preferably identical. Thevelocity V is the velocity with which the row of excavation wheels ismoved and is directed in the same longitudinal x-direction for the wholelattice construction and thus for all excavation wheels. The resultingtangential forces (soil reaction), respectively Ft1 and Ft4, aresupposed to be substantially identical with regard to magnitude anddirection. In the same way the tangential forces Ft2 and Ft3 aresupposed to be substantially identical with regard to magnitude anddirection. All the resulting radial forces (soil reaction), respectivelyFr1, Fr2, Fr3, and Fr4, are supposed to be substantially identical withregard to magnitude and direction.

The resulting forces and moments that are being exerted onto the latticeconstruction (3) are as follows:

-   -   the moment in the XZ-plane: Mxz=Ft1*Y0=Ft2*Y0, in which Y0 is        the distance in the Y-direction from the centrelines of the        respective excavation wheels 51, 52 (or between the excavation        wheels 54 and 55)    -   the resulting force in the radial direction,        Fr=2*Fr1=2*Fr2=2*Fr3=2*Fr4    -   the resulting bending moment around the Y-axis:        My=(Fr1+Fr2+Fr3+Fr4)*Z−gv=4*Fr1*Z−gv, in which Z−gv is the        distance in Z-direction from the centreline in Y-direction of        the excavation wheels (51,52,54 and 55) and the centreline of        the bottom part of the lattice construction (3).

The resulting forces and moments that are being exerted onto the latticeconstruction (3) are identical with regard to magnitude and direction,with the exception of the moment Mxz in the XZ-plane, which works inopposite directions via the boxlike constructions (53, 56).

The resulting bending moment that is exerted onto the associated boxlikeconstructions via the excavation wheels by the resulting soil reactionFt1=Ft2=Ft3=Ft4 is reduced with regard to the order of magnitude to avalue of My=Ft1*Z−gd*sin α=Ft4*Z−gd* sin α, and the oppositely orientedbending moments −My=Ft2*Z−gd*sin α=Ft3*Z−gd*sin α (see FIG. 6). Thedistance Z−gd is equal to the vertical distance between the centre lineof the excavation wheels (51, 52, 54, 55) and the centre line of theboxlike constructions (53, 56). The angle α is equal to the anglebetween the tangential soil reaction force Ft_1 and the vertical.

The resulting bending moment on the lattice construction due to thetangential soil reaction forces (Ft1, Ft2, Ft3, Ft4) is negligiblysmall. The resulting horizontal force upon the lattice construction (3)and upon the bridge part (22) that has to be exerted onto the bridgepart (22) by the winch cables (23) due to the forces on the excavationwheels is equal to Fx=4*Fr1* sin 60 , which represents a relativelysmall value.

FIG. 6b shows a pair of excavation means of row (34), as well as a pairof excavation means of row (35), seen from beneath. The referencenumbers have the same meaning as in the foregoing figures. The beam (3e) is a protective construction. The figure shows how parts of thebottom of water that are situated between the excavation means of row(34), and therefore cannot be excavated efficiently by the row (34), canthen be excavated by the excavation means of the adjacent row (35).

FIG. 7a shows a guiding tube (20) of the bridge part (22) through whichthe framework beam (16) passes, as can be seen in FIG. 2. In the figurethe framework beam (16) is represented somewhat withdrawn, in such a waythat the inner side of the guiding tube (20) is visible. The inner sideof the guiding tube (20) comprises resilient wheel sets (60) that permita displacement of the bridge part (22) along the framework beam (16) inthe longitudinal direction. The wheel sets (60, 64) are implemented insuch a way that they also, during use, permit six kinematic degrees offreedom from the guiding tube (20) in the radial, tangential, androtational (around the vertical axis) direction relative to theframework beam (16). Such a degree of freedom for the guiding tube (20)with regard to the framework beam (16) is important and avoids clampingforces when the bridge part (22) that can be seen in FIG. 2 is movedalong the framework beams (18, 19) by the winches (23). The frameworkbeam (16) is composed of three parallel tubes (61) that form atriangular cross-section and a rigid entity. The outside of thesecombined tubes (61) comprises a flat plate (62) that comprises a rail(59) on which the wheel sets (60) can roll. The three tubes (61) and theflat plate (62) together form a cross-section that resembles thetriangle of the framework beams (16).

FIG. 7b shows a cross-section of the framework beam (16) and of theguiding tube (20), in which the interaction between the guidingtracks/rails (59) that are uniformly distributed along the circumferenceof the framework beam (16) and connected thereto, and the resilientwheel sets (60, 64) can be seen. The flat plates on which the point loadof the guiding wheels is being exerted can be strengthened by usingradial plate elements (59 a) or tubes (59 b) that fit in the open spacesof the circumference of the framework beam (16) and the combined tubes(61).

FIG. 7c shows a cross-section of the framework beam (16) and of theguiding tube (20). The resilient wheel sets are in this case resilientrollers (69 a) that are resiliently suspended from a wheelset, as can beseen from FIG. 8 c.

FIG. 8a shows the wheel sets (60, 64) of FIG. 7 in further detail. Thewheelset (60) comprises a U-form baseplate (62). The baseplate (62) isfixed by its bottom side to the inner side of the guiding tube (20), insuch a way that the raised extremities of the U-form baseplate aredirected towards the inner sides of the guiding tube (20). Between theraised extremities of the U-form baseplate (62) a system (63) with fourwheels is resiliently clamped by means of springs (65). The system (63)with four wheels in turn forms the basis of a wheelset (64) of which thewheels (67) are perpendicular to the direction of the wheels of thesystem (63) with four wheels. The wheelset (64) of which a wheel (67) ispart, is fixed onto the stationary axes (66) of the system (63) withfour wheels, and is, thanks to the vertical springs (65 a) of thewheelset (64), capable of absorbing a movement in the radial direction.The wheel (67) of the wheelset (64) makes contact with the guiding rails(59) that are fixed to the outside of the framework beam (16), as can beseen from FIG. 7a , and permits, during use, a passage in theX-direction. Thanks to the resilient suspension of the system with fourwheels upon which the wheelset (64) is positioned, the wheelset (64) cancarry out a small displacement in a substantially tangential direction(Y-direction in FIG. 8a ) relative to the inner side of the guiding tube(20) on which the wheelset (60, 64) is mounted.

FIG. 8b shows in further detail how the wheelset (64) from FIG. 8a canundergo an angular displacement Ψ in the radial direction, in such a waythat the forces on the wheels (67) and on the guiding rails (59) of theframework beam (16) are strongly reduced.

FIG. 8c shows a roller (69 a) that is resiliently connected to two wheelsets (60) by means of springs (65 a), as discussed with regard to FIG. 8a.

FIG. 9 schematically shows how the extremities of the framework beams(16, 17) and the extremities of the transverse beams (18, 19) areresiliently connected to a corner in each of the four corners(24,25,26,27) of the rectangular frame (15). The sleds (33) areresiliently (73) connected to the corners (24,25,26,27), in such a waythat, when the rectangular frame (15) is anchored to the bottom ofwater, the rectangular frame (15) comprises a resilient geometry withsix kinematic degrees of freedom. The resilient connection of theframework beams and the transverse beams with the corners is realised bymeans of a ball joint (70), a connector (71), and a spring (72). Theball joints (70) permit limited angular displacements (φ2, θ2, ψ2) ofthe framework beams (16, 17) and of the transverse beams (18, 19)relative to the corners (24,25,26,27). The displacements of the corners(24,25,26,27) in the horizontal XY-plane are made possible bycompressing or extending spring elements (72) and by the angulardisplacements of the ball joints (70). In order to permit the sleds (33)to follow the contours of the bottom of water properly, the sleds havekinematic degrees of freedom (x, y, z, φ, θ, ψ) that can be realised bymeans of a spring (73), a hydraulic cylinder (74), ball joints (70), andthe springs (72) of the corners (24, 25, 26, 27). Because of thekinematic degrees of freedom (x, y, z, φ, θ, ψ) of the sleds (33) thesleds are capable of, in case of horizontal displacements of theframework (15), following the contours of the bottom of water properly.Moreover, the moments at the corners (24, 25, 26, 27) will be stronglyreduced by the flexibility of the framework (15). The displacements (Y7,Z7) and the angular displacements (φ7, θ7, ψ7) of the bridge part (22)are realised by the translating and rotating resilient wheel sets (60,64) that can be seen in FIG. 7a-c , and a longitudinal displacement (X7)by means of the winches (23). The applicant has found that, when such aframework (15) is anchored to the bottom of water, a very rigid and formstable framework is obtained that permits an unhindered displacement ofthe bridge part (22) along the framework beams (16, 17).

FIG. 10-13 shows a possible embodiment of a bridge (84). In order torealise a large vertical displacement of the rows of excavation meansrelative to the framework (15), the rows of excavation means (34, 35),the lattice construction (3), and the boxlike construction (5) are partof a telescopic construction. FIG. 10 shows this construction, in whichthe rows (34, 35) are completely lifted by means of the winch cables(80), the hydraulic cylinders (81), the hydraulic cylinders (82), andthe hydraulic cylinders (7). The winch cables (80) can move the latticeconstruction (3) and the therewith connected rows of excavation means(34, 35) in a vertical direction relative to a bridge part (84). Thewinch cables (80) also provide a rotational stability for the boxlikeconstruction (5) around the axis that passes through the boxlikeconstruction, from the framework beam (16) to the framework beam (17)(see FIGS. 1 and 2).

The bridge part (84) is a modified bridge part (22) and also comprisesguiding tubes (not represented) to be able to move along the frameworkbeams. The bridge part (84) comprises hydraulic cylinders (81) that canvertically move a boxlike construction (85). The boxlike construction(85) is open at its top side and at its bottom side. The boxlikeconstruction (5) comprises four upright walls (86) that in turn compriseresilient guiding wheels (87) for guiding the inner wall of the openboxlike construction (85). The inner walls (88) of the rectangularopening in the bridge part (84) also comprise resilient guiding wheels(89) for guiding the external wall of the open boxlike construction(85).

FIG. 11 shows the open boxlike construction (85), which has been moveddownwardly by retracting the hydraulic cylinders (81).

FIG. 12 shows the boxlike construction (5), which has been moveddownwardly by extending the hydraulic cylinders (82).

FIG. 13 shows the lattice construction (3) and the therewith connectedrows (34, 35) of excavation means that have been moved downwardly byretracting the hydraulic cylinders (7). Such a bridge, as can be foundin FIGS. 10-13, can be part of a submersible framework (15) as a movablebridge part. The framework beams and the transverse beams can be filledwith air in order to move the framework (15) from the bottom of water tothe water surface.

FIGS. 14a-d show an excavation installation according to the inventionin which the bridge (5) is resiliently connected to a floating vessel(90) by means of four hydraulic cylinders (91), at the top sidecomprising springs that extend downwardly from the floating vessel (90)to the bridge (5). FIGS. 14a-d show a single row (34) of excavationmeans. The excavation means shown in FIGS. 14a-b are trailing dredginghead (34 c). The bridge (5) can also be a telescopic bridge, as can beseen in FIGS. 10-13. Each of the four hydraulic cylinders (91) is at thetop side connected to the vessel (90) by means of a ball joint (92), andat the bottom side connected to the bridge (5) by means of a ball joint(93). A lattice framework (100) is connected to the vessel (90).

The ball joints (92) can, via the lattice framework (100) by means of acylinder (101), move in a parallel way to the direction of the row ofexcavation means. Thus, the direction of the cylinder (91) relative tothe bridge (5) can be kept substantially in a vertical position when thefloating vessel rolls due to swell. The length of the cylinders (101 and91) shall be adjusted in response to or anticipation of the movement ofthe floating vessel in such a way that the excavation means can bepressed onto the bottom of water with a substantially constant verticalforce. The spring at the top of the cylinder (91) is preferably inpossession of a smaller spring constant than that of the hydrauliccylinder. Using this construction, one obtains a complete decoupling ofthe movements of the floating vessel (90) from the bridge (5), but thenecessary vertical pressing force on the excavation means is maintained.The other extremity of hydraulic cylinders (91) is connected to thebridge (5) by means of ball joints (93). By means of the cylinders (91)the aforementioned bridge (5), the therein integrated hydrauliccylinders (7), the columns (6), and one or two rows of excavation means(34 and/or 35) can be lifted off the bottom of water (102) or positionedon the bottom of water (102). The water surface (103) is also drawn inthe figures. The bridge (5) comprises four upright walls (104) that,using multiple springs (107, 109) and roll bearings (105, 108), areenclosed along the walls in an opening (106) of the floating vessel(90). Thanks to this resilient suspension of the bridge (5) smallrolling and pitching movements of the vessel (90) due to the swell canbe absorbed.

FIGS. 14e-f show an excavation installation according to the inventionin which the bridge (5) is resiliently connected to a floating vessel(90) by means of four hydraulic cylinders (91), from which eachhydraulic cylinder (91) is connected to a horizontal plate (91 b), whichis connected to three hydraulic cylinders (91 a). For decoupling themotions of the vessel (90) and the bridge (5) the three cylinders (91 b)at each corner of the bridge (5) are connected to both the horizontalplates (91 b) and the portal of the vessel (100 a) by means of balljoints (93 a). The three hydraulic cylinders (91 a) preferably will bein a vertical direction and will be controlled in such a way that theposition of the horizontal plate (91 b) in the horizontal x-y plane,within a narrow deviation, is equal to the position in the x-y plane ofthe bottom of the hydraulic cylinder (91), which is connected to thebridge (5). The hydraulic cylinders (91) are connected to the horizontalplates (91 b) and the bridge (5) by means of ball joints (93 b). Allhydraulic cylinders (91 a) and the hydraulic cylinders (91) should beable to withstand the resulting vertical force initiated by theexcavating means (1,2) in rows (34,35) and the vessel (90) motionsrelated to the bridge (5) position. The propulsion propellers (145) ofthe vessel (90) are synchronized with the propulsion propellers (146)connected to the lattice (3) in such a way that the velocity of thevessel (90) equals the velocity of the lattice (3). Connected to bothsides of the bridge (5) are excavating means (34 a, 35 a), which areconnected to lattices (3 a) and can be displaced vertically usingcolumns (6 a) which are connected to hydraulic cylinders (7 a). Thefunction of both excavating means (34 a, 35 a) is to stabilize theexcavated trench on both sides in transverse y-direction. Such means (34a,35 a) may also be used in combination with a frame (15) as in FIG. 2.

The suction of the soil/water mixture of the excavation means (1,2) inrows (34,35), especially in shallow waters, is realized usingcentrifugal pumps (144) which are connected to the lattice (3). Also theflow of the soil/water mixture of side excavation means (34 a, 35 a) isrealized using centrifugal pumps (not presented in the figure), whichare connected to the lattices (34 a) and are connected to a verticaldisplaceable suction tube (4 a), in a way similar to the suction tubes(4) of the excavation means (1,2).

FIG. 15 shows how the submersible and rectangular framework (15) of FIG.2 is anchored by means of screw anchors (33 a) to the bottom of water(102) and at a large depth below the water surface (103). In FIG. 15aone can see how the bridge part (22) is moved from right to left bymeans of winch cables (23). In doing this, the rows (34, 35) ofexcavation means create a trench (104). In FIG. 15b one sees the bridgepart (22) in its uttermost left position after which, from a stationaryposition, the excavation means are given a small vertical initialmovement by the force of the hydraulic cylinders on the latticeconstruction (3), after which the direction is reversed and theexcavation means, the hydraulic cylinders, the columns, and the bridgepart (22) are moved to the right by means of the winch cables (23). Thenext layer of the bottom of water is then excavated and a deeper trench(104) is created, as can be seen in FIG. 15c . The dashed lines in FIG.15 indicate which compartments are filled with water, in which the finedashed lines in the framework beam (16) indicate that air is present inthe two upper tubes (61) and water in the bottom tube (16).

FIG. 16 shows how the rectangular framework (15) from FIG. 2 can beconnected to a floating vessel (110) by means of a framework (111) andfour cylinders (112). The four cylinders are connected to the corners(24, 25, 26, 27) and to the framework (111) in the same way as can beseen in FIG. 2. In the figure the anchors and the supporting means arerepresented. It should be absolutely clear that these anchors andsupporting means in this embodiment have no function. However, it is notimpossible for the framework (15) to be alternatively used in theembodiment according to FIG. 16 and in the embodiment according to FIG.15. By decoupling the cylinders (112) in the corners (24, 25, 26, 27)the framework can be easily submersed and moved away and positionedunder the floating vessel (110).

FIG. 16 also shows two floating barges (114) in which the excavated soilcan be collected. By means of pipes and tubing (113) the excavated soilcan be transported to these barges by means of pumps (not represented)in the framework (15) or fixed to the lattice construction (3).

FIG. 17 shows an excavation wheel (1) that comprises a bottomcompensator that is made up of two spherical hoods (121) that arepivotably connected to the rotation axis of the wheel (1). If theexcavation wheel encounters an obstacle on the bottom of water, as isrepresented in FIG. 17 by means of the force Fg, the sphericalconfiguration of the hood (121) shall impart an upwardly directed forceonto the excavation wheel. Part of this force will be absorbed bysprings (120) with which the hood at its upper end is connected to thebox like construction (39).

FIG. 18a shows how an excavation wheel (1) is connected to the latticeconstruction (3), rotatable around the axis in the transverse direction.For this, the lattice construction (3) comprises a rigid part (3 a) anda pivotable part (3 b). The pivotable part (3 b) is in turn connected tothe excavation wheel (38), as can also be seen in FIG. 5a . Therotatable axis (141) comprises rigid torsion springs (140).

FIG. 18b shows how an excavation wheel (38) is connected to the latticeconstruction (3) by means of a cardan joint. The excavation wheel is nowrotatable around an axis (141) in the transverse direction, and alsorotatable around an axis (143) in the longitudinal direction, and isconnected to the lattice construction (3). The axes (141, 143) compriserigid torsion springs (respectively 140 and 142), in such a way that thepivotable parts (3 b and 3 c) of the lattice construction are returnedto their horizontal position, for example after an impact on theexcavation wheel (1).

1. Excavation installation, comprising excavation means in which morethan one excavation means is positioned next to another in a row ofexcavation means, in which multiples of such rows of excavation meansare positioned behind one another, and in which the excavation means ofa particular row are offset with regard to the excavation means of anadjacent row, such that in use the excavation installation may excavatea horizontal bottom of water in a direction that is perpendicular to thedirection of the rows of excavation means, in which the excavation meansare connected to a rigid construction positioned vertically above theexcavation means by means of a resilient connection in order to absorbthe vertical impact loads on the excavation means and to transmit theseimpacts to the rigid construction, and in which the rigid constructionis resiliently connected to a bridge that is positioned vertically abovethe rigid construction, in which the bridge is connected to the rigidconstruction by means of linear actuators, in such a way that, duringuse, the linear actuators exert an adjustable and vertical pressingforce onto the excavation means.
 2. Excavation installation according toclaim 1, in which the bridge comprises a box construction.
 3. Excavationinstallation according to claim 1, in which the bridge is movable alongparallel framework beams that are positioned in a longitudinaldirection, that together with two transverse beams form a framework. 4.Excavation installation according to claim 3, in which the movablebridge is connected to the two transverse beams by means of winchcables, in which the winch cables permit a longitudinal movement of themovable bridge along the two parallel positioned framework beams. 5.Excavation installation according to claim 3, in which the movablebridge at each of its extremities comprises a guiding tube, in whichthrough the opening of each of these tubes passes one of the twoparallel positioned framework beams, such that the movable bridge canmove in the longitudinal direction of the framework beams.
 6. Excavationinstallation according to claim 5, in which the guiding tubes at theirinner sides comprise resilient wheel sets and/or resilient rollers that,during use, can give the framework beams six kinematic degrees offreedom relative to the guiding tube.
 7. Excavation installationaccording to claim 3, in which the corners of the framework comprisemeans for anchoring the rectangular frame to the water bottom. 8.Excavation installation according to claim 7, in which the corners ofthe rectangular frame comprise a supporting means.
 9. Excavationinstallation according to claim 3, comprising one or more means formoving the rectangular frame.
 10. Excavation installation according toclaim 3, in which the extremities of the framework beams and theextremities of the transverse beams are resiliently and by means of aball joint connected to a corner in each of the four corners of therectangular frame, in which the means to anchor the rectangular frameare resiliently connected to the corners, and in which the optionalsupporting means are resiliently connected to the corners. 11.Excavation installation according to claim 3, in which the excavationinstallation is submersible.
 12. Excavation installation according toclaim 11, in which the framework beams, the transverse beams, thecorners and/or the movable bridge comprise compartments that can befilled with gas and/or water in order to float or submerse theexcavation installation.
 13. Excavation installation according to claim1, in which the bridge is resiliently connected to a floating vessel bymeans of multiple linear actuators that extend from the floating vesselin a downward direction towards the bridge, and in which the ends of theactuators are connected to the bridge and to the floating vessel bymeans of ball joints.
 14. Excavation installation according to claim 1,in which the excavation means are positioned in two or three rows behindone another.
 15. Excavation installation according to claim 1, in whicha row with excavation means comprises 3 to 30 excavation means. 16.Excavation installation according to claim 1, in which the excavationmeans are excavation wheels, drum cutters, drag heads, cutters and/orploughs.
 17. Excavation installation according to claim 1, in which theexcavation means comprise wheels that rotate around a substantiallyhorizontal axis, in which the excavation means are positioned in pairsin a row, and in which the rotating wheel of the first excavation meansof a pair, during use, rotates in a direction that is contrary to therotating direction of the rotating wheel of the second excavation meansof the pair.
 18. Excavation installation according to claim 17, in whichthe rotating wheel of the first excavation means of a pair is anovercutting wheel and the rotating wheel of the second excavation meansof the pair is an undercutting wheel.
 19. Excavation installationaccording to claim 17, in which the excavation means are connected to arigid construction in pairs, in which the rigid construction ispositioned vertically above the excavation means and is connected bymeans of a resilient connection to the pairs of excavation means inorder to absorb the impact loads and the continuously varying andfluctuating loads on the pair of excavation means and to transmit theseimpact loads to the rigid construction.
 20. Excavation installationaccording to claim 1, in which each of the excavation means is connectedto a suction tube for discharging the mixture of soil and water that hasbeen excavated by the excavation means. 21-26. (canceled)